Why isn't my mesh properly textured in Blender.
Well, it's hard to tell exactly without seeing the actual .blend file or a screenshot of the various steps you used, but i'll guess that:
... You either didn't separate the various mesh sections physically  or by using "seams", before unwrapping, then selecting specific faces before assigning the materials....
.. or by designating and assigning "vertex groups" to define various sections before "applying" or "assigning" the materials on the "edit level",
... or used an inappropriate or "singular" method of "UV Uwrapping" for the various parts,
... or didn't just "paint your textures" on using the live "texture painting" option after doing a "basic" UV UnWrap....

To fix, you might want to go back into Edit mode and establish "marking seams" to separate the various parts not just by texture or color, but be sure to include an additional splitting seam to allow the Unwrapped sections to flatten out properly for proper "fitting" of the texture to those specific areas... ...If you do this correctly your Unwrap should look like a pattern used for cutting out sewing panels...
....If you did that part correctly, you can use the texture paint tools to "live paint" the textures in 3D or hand paint the various parts of your unwrapped UV mesh islands...
....If you select various faces at a time, you can assign "Vertex Groups" (under the Mesh or "vertex" Data panel) to just those faces, lock them, then unwrap by "View Projection" or whatever method is appropriate, give "that" resulting UVMap it's  own unique name in the "vertex panel as well", assign a material containing the desired texture, and making sure that the desired "unique UVMap" name is chosen under the texture "mapping" options...   ...Then be sure to "deselect" the new vertex group before creating and assigning the next and repeating the process....
...Review a tutorial on UV-unwrapping and texturing a Character as the proper material for your Renderer.... mixing BI material nodes with Cycles doesn't work well....
...If you have the Matcap materials option turned-on on your view Display options, that could also be interfering with what your models surface appearance...
...Hope that helps a bit...